Proline and Polyamine Involvement in Chilling Tolerance of Maize Suspension Cultures

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Abstract
We have assessed the effect of various medium supplements in promoting the ability of maize (Zea mays L.) inbred FR27rhm suspension cultures to grow following a period of 4 °C chilling stress. Following a 4 week exposure to 4 °C in culture medium without proline, no cell growth occurred upon subsequent incubation at 28°C for 2 weeks. This inhibition was reversed when 3 to 48 mol m−3 proline or 0.1 mol m−3 putrescine or 0.01 mol m−3 spermidine were present in the medium during the chilling stress. On the other hand, suspensions were made more sensitive to 4°C by blocking polyamine biosynthesis with 1.0 mol m−3 methylglyoxal bis (guanylhydrazone) (MGBG) or a combination of 1.0 mol m−3 difluoromethylornithine (DFMO) and 1.0 mol m−3 difluoromethylarginine (DFMA). The addition of 10 mol m−3 putrescine to the suspension containing DFMO and DFMA prevented the increased chilling sensitivity. Electrolyte leakage studies conducted to assess membrane integrity after 4 weeks at 4°C and a 2 week regrowth period showed that cells treated with no polyamines (control), 0.01 mol m−3 spermidine, 1.0 mol m−3 putrescine, or 1.0 mol m−3 MGBG lost 43, 32, 14, and 100% of the total electrolyte pool, respectively. These results suggest that proline and polyamines are beneficial for inducing chilling tolerance in FR27rhm suspension.